A 777-200, state of the art in 2000, has an optimum hop distance of about 5,600 km. That's the distance where the fuel use per passenger mile is minimum. For example:GRA wrote: ↑Fri Nov 15, 2019 4:25 pmhttps://www.withouthotair.com/cC/page_278.shtmlOptimizing the hop lengths: long-range planes (designed for a range
of say 15 000 km) are not quite as fuel-efficient as shorter-range planes,
because they have to carry extra fuel, which makes less space for cargo
and passengers. It would be more energy-efficient to fly shorter hops in
shorter-range planes. The sweet spot is when the hops are about 5000 km
long, so typical long-distance journeys would have one or two refuelling
stops (Green, 2006). Multi-stage long-distance flying might be about 15%
more fuel-efficient; but of course it would introduce other costs.
The technical chapter on flight of the above, Chapter C, runs from page 269-282.
The reference is to this:Unfortunately I haven't been able to find a version that isn't behind a paywall.Green, J. E. (2006).
Civil aviation and the environment – the next frontier for the aerodynamicist. Aeronautical Journal, 110(1110):469–486.
A 787 has an optimum hop distance of about 7,300 km
Calling trips beyond the optimum hop distance inefficient is making several assumptions that are usually not realistic.
There likely isn't an airport right under your direct flight path at the ideal distance to stop on, so adding the stop adds distance. This also makes the legs different lengths. This can be complex, as there can be many choices, and the aircraft might be different on different legs.
A 777-200 flight to 3000 nm compared with two 1500 nm legs, the two legs are not cheaper. (look at above graph)